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The current study reports LaFe1-xMnxO3−δ redox catalysts (RCs) for CO2-splitting and methane partial oxidation (CH4-POx) in a cyclic redox scheme. Lanthanum (La) was chosen as the A-site cation whereas iron (Fe) and manganese (Mn) were chosen as the B-site cations, respectively. La, Fe, and Mn were incorporated into the perovskite structure (LaFe1-xMnxO3−δ) at various Fe/Mn ratios to tailor the equilibrium oxygen partial pressures for CO2-splitting and methane partial oxidation. Compared to the standalone redox pairs of Fe and Mn (i.e., Fe2O3/Fe3O4, Fe3O4/FeO, and Mn2O3/Mn3O4) which, from a thermodynamic standpoint, favor the complete combustion of CH4, the perovskite structured redox catalysts (RCs, i.e., LaFe1-xMnxO3−δ) favored the selective oxidation of CH4 to syngas. In addition, impregnating the RCs with 1 wt% ruthenium (Ru) led to a significant improvement in their redox kinetics without affecting their redox thermodynamics. The Ru-impregnated, perovskite structured RCs (i.e., LaFeO3, LaFe0.625Mn0.375O3, and LaFe0.5Mn0.5O3 ) exhibited excellent redox performance in terms of the syngas yield (92 – 100%) and CO2 conversion (95 - 98%). Long-term redox testing over Ru-impregnated LaFeO3 and LaFe0.5Mn0.5O3 demonstrated relatively stable performance for 100 redox cycles whereas activity loss was observed for LaFe0.625Mn0.375O3, LaFe0.375Mn0.625O3, and LaMnO3 respectively. Among RCs containing both Mn and Fe, LaFe0.5Mn0.5O3 exhibited the best performance, maintaining satisfactory activity over 100 cycles and higher oxygen capacity. XRD and XPS analysis suggest that the ability to regenerate the perovskite phase under a CO2 environment and a near surface A:B site cation ratio close to the perovskite stoichiometry would likely correspond to more stable performance. Additionally, the inclusion of Mn on the B-site enhances the coke resistance of the redox catalyst when compared to undoped LaFeO3. 

A series of perovskite oxides (Ln = La, Pr, Nd, Gd; A = Ba, Sr) was investigated to understand the effects of A-site cation size on oxygen vacancy formation. Quasirandom mixed structures were generated using Alloy Theoretic Automated Toolkit (ATAT), followed by density functional theory (DFT) calculations. While mixing the orthorhombic structures with the hexagonal AMnO3 structures leads to lattices and global symmetries closer to cubic, the average volume generally increases with the average ionic size, and the local bond and angles exhibit more variations due to A-site mixing. DFT calculations and a statistical model were combined to predict oxygen reduction abilities. Thermogravimetric analysis (TGA) provided experimental validation of these predictions by measuring changes in oxygen non-stoichiometry under controlled conditions. Both indicated that larger A-site ionic size differences lead to greater, consistent with the larger variation in local structures, and enhanced redox capabilities. This combined computational-experimental approach highlights the importance of local structure variation, instead of average properties, in A-site cation engineering to optimize perovskite oxides for different devices relying on oxygen vacancy redox activity.